Process for insulating magnetic bodies



its. COMPOSITION/IS, GROSS Emma comma I UNITED STATES-PATENT orr csHUBBEL LATHBOP, or enmwrcn, colmncrrcu'r, .ASSIGNOB "r BELL rnnnrnoma-LABORATORIES, mcoarom'rm), on NEW YORK, N. 2., a conronnrron or NEW Yonxa t rnocnss on msunn'rme menn'rrc nomns in Drawing. Application and mya, 1931. Serial 110. 548,484.

.This invention relates to magnetic bodies form, and a volatile li uidsuch as wajzgr, and particularly to methods of producing and then toevaporate the whole to dFy ness magnetic bodies of the ty eemployingfinely with constant stirring in order to coat the dividedmagnetic matena l; magnetic particles with the-insulating mate- Anobject of the invention is to improve the rial. The total amount ofinsulating material magnetic characteristics of magnetic bodies is thusapplied to the magnetic dust particles of the type employing magneticmaterial in In one layer. The insulated magnetic pa'r-' finely dividedform, for example, magnetic ticles are then compressed under hi hpresdust cores for loading coils. sure into the desired core form, anthe re- 1 Magnetic cores made from finely divided sulting cores aregivenasubsequent annealing magnetic material, so-called magnetic dustheat treatment to improve their magnetic cores, are being extensivelyused for the loadlfl erl csing coils which are inserted in telephonelines In accordance with the resent invention to improve theirtransmission characteristics. the rocess of insulation a ove describedis L 15 Such cores are usually constructed by submodified in that theipgulating material is a jec'ting the finely divided particles of thelied to themagp etic dggpapt clesapofi on magnetic material and anon-magnetic matea a times?) as to' obtam several layers ofthe rialbetween the magnetic particles, to ex samemsulating material between themagtremely high pressures in the neighborhood n ic part cl Th ch ng inthe m t go of 200,000 pounds per square inch. The high of insulating hasbeen found to materially pressures are utilized to form the componentimprove the magnetlc properties, and particuv materials into asubstantially homogeneous larly to reduce the eddy current loss in themass in the desired core form, and to give sufcompleted core. ficientmechanical strength to the completed The exact nature of the inventionand the as core. The non-magnetic material is of such advantages thereofwill be better understood a nature as to serve as a binder, andalso asfrom the following detailed description of an insulation between themagnetic particles the process for producing a magnetic dust to reduceeddy current losses in the completed core or a loading coil embodyingthe inven-' core., 'In the-case especially where the magtion.

a netic material in the core made in the above In practicing the presentinvention, the described manner is a magnetic alloy includmagneticmaterial is preferably prepared ing nickel and iron, it is desirablealso to subfrom a brittle alloy containing nickel and ]ect the core tosubsequent heat treatment at iron, with or without the addition of othera high temperature to remove the strains inconstituents, and commonlyknown aW SI troduced in the magnetic material by the alloy The-alloy maybe prepare 1n e pressing operationtending to impair them described inthe U. S. Patent No. magnetic properties of the magnetic alloy in1,669.649 issued May 15, 1928 to (LP. Beaththe core. and to fullydevelop the magnetic and H. M. E; Heinicke, wherein themagcharacteristics of the alloy. It is desirable, netic metals, forexample, nickel and iron in 40 therefore, that the insulating materialhave proportions depending upon the desired persuch characteristics andbe applied in such centage of the alloy, are melted together in mannerto the dust particles that it will withsin-oxidizing atmosphere, theresulting alloy stand without deterioration from an insulatbeing pouredinto a mold to form an ingot. ing standpoint the heat treatment and'me-The-ingot while still hot is successively passed v chanical operationsutilized in producing the through progressively reducing rolls todecore. a crease its cross-section, the final roll being Amethodcommonly used for insulating the preferably efiected at approximatel thetemma netie dust in the process of making loadrature at which the alloceases to mallea mg coil cores is to mix the magnetic dust 1e, afterwhich the ingot 1s quenehedinwater with the insulatim in finely dividedat a temperature below that in which it loses i th solution of SQd nm.sili cm, and chromic 15 a ball mill for several hours.

46 of the annealed finely silicatp in sol utip n with 1.1 grams ofchromic Each 1000 grams of 55 mixed with 2.5 grams el 60 stirring,

its malleability. This treatment is for the purpose of producing a finecrystalline struc ture in the allo material since when the material isreduce to finely divided form its disintegration takes place at thecrystal boundaries, and conse uently the smallerthe size of the crystalsthe finer the dust which can be produced therefrom. The slabs of-alloymaterial 'so produced are then broken into short pieces and the piecesreduced to the form of dust in any suitable manner for example bycrushing in a rock crusher, hammer mill, or other suitable apparatus,after which the crushed material is pulverized by rolling in Afterseveral hours of rolling the resulting dust is sieved through a 120 meshsieve and that portion which will not pass through the sieve is returnedto the ball mill for further rolling, go this process being repeateduntil a 'sufiicient uantity of the very'fine dust is obtained.

r-iorto the addition of the insulating material the finely dividedarticles of the alloy are annealed in a closed container at atemperature of approximately 885 C. It is then necessary to again reducethe annealed alloy which is now in the form of a cake to a finely.

divided iorm ready for insulation.

' The general method of insulating the magnetic particles in accordancewith this invention was tried with several insulating com- 1 positions.In each case a material improvement inthe magnetic properties of thecompleted core was observed over that obtained when the usual method ofinsulation was employed.

' In one case the method of the invention was applied to the insulationof the annealed magnetic articles with an i sulatin com 081- 40 tloncomprislng lggglgm talc @E upfi s i licte, F cliromlc acetate andwaterfieuc as isclosed 3 an speci ca y claimed inmy co plication, SerialNo. 556,951, file August .14,

1931. It was desired to insulate 1000 grams rmallo d 1 1 st with a totalof 6.5 grams fine y ivided kaolin, 6.5 grams ivided talp and 11.0gramsof sodium ioetat This was done as follows: I 5 .The 11.0 grams of sodiuni sili cate and 1.1 f grams of chromic acetate were first dissolved inwate'r toTt'otal s olution volume of 333 cc.

v1 ed talc and 2.5 grams finely divided aolin .11I cc. of

' Then, an' additional 2.0 grams talc and 2.0

grams kaolinwere mixed witE the coated magnetic particles an additional111 cc. of

the

solution added thereto, and the whole sodium silicate. One third-o dingaptransferred to an annealin rmallo dust were then evaporated again to dess with constant st1rr1ng,"toform a secon "1a" "er of insulation on thepermallo dustparticles. Then the resulting coate magnetic particles weremixed with the remaining 2.0 grams talc and 2.0 grams kaolin, theremaining HT 6c. of the solutiofi'a'dded thereto, and the wholeevaficTfia'fEd to dryness to form a third layer of insulation on themagnetic particles.

In another case it was desired to insulate the annealed permalloy dustwith an insulating composition such as disclosed in my copendingapplication, Serial No. 459,564 filed June 6, 1930. The insulatingmaterial used comprises 1.6 grams sodium silicate and 1.0 grams tale foreach ams of the ma etic diTstT A solutiono the sodium silica fi in waterwas first made up, 40 cc. of waterbeing used for each 1.6 rams of thethe tale in dry powder form was then mixed with the total amount of thepermalloy dust, one third of the sodium silicate so ution was added themagnetic particles. The insulate 'mag- I netic particles were then mixedwith another one third of the tale, another one third of the sodiumsilicate soliition was added thereto and the resulting mixture was againevaporated to dryness to form the second coating of the insulatingmaterial on, the magnetic dust .particles. The remaining one thirdortion of talc was then mixed with the insuated maone thir of the sodiumsilicate solution was added thereto and then the resulting mixture wasevaporated todryness to form the third coating of insulating materialupon the magnetic particles.

above described manner were respectively etic dust particles, theremaining flhe magnetlc dust particles insulated with the difierentinsulating compositions in the sifted through a 16 mesh sieve, placed ina.-

mold and compressed into core partsunder a pressure of approximately200,000 pounds per square inch. The core parts were then furnace wherethey were annealed at a high temperature either in airor in hydrogen torelieve the internal stresses set up by the pressing operation, therebyproducing a core having low hysteresis loss. I

Where the annealing heat treatment is carried out in air, the core partsare preferably subjected to a temperature of approximately 500 C.forabout 45 minutes. Where the'annealing heat. treatment is carried outin hydrogen,.the core parts are preferably subjectedto a temperature ofapproximately 650 C. for about 30 minutes. a

One or more core parts thus formed are then stacked to form a coreto'which the usual toroidal winding'is applied to form a loading coil,the number of core parts used in I06. COMPOSITIONS,

COATING ORPIASUC 'inpi coil is to be associated.

each core depending u on the electrical char-' acteristics 0 the circuitwith which the loadestsof magnetic cores insulated by the method of theinvention in which the insulating material ,was applied in three or morestages as described above and other cores made at the same time usingthe same amount and kind of insulating material applied in" a singlelayer by the usual method, showed that the former method resulted inmuch lower eddy current losses in all cases and in most cases inimproved hysteresis characteristics not limited to the particularconstituents and proportions of the magnetic and insulating materialsabove mentioned which were given by way of example only, but that it isof a eneric nature applicable to all magnetic and insulating materialswhich are commonly used in the production of magnetic bodies of the typeemploying magnetic material in finely divided form. It is to beunderstood also that the method of applying the insulatmg material maybe varied somewhat from that described above without departing from thespirit of the invention which is limited only within the scope of theappended claims.

a What is claimed is:

1. In the'process of makin a magneto body comprising finely dividedmagnetic particles insulated from each other by a given, amount ofinsulating material, the method of insulating the magnetic particleswhich-consists in mixing sa1d particles with a portion of the insulatingmaterial in a volatile liquid and evaporating the mixture to d ness, andmixingthe resulting product wit another portion of the insulatingmaterial in a volatile lii uid and evaporating to dryness.

n the process of makin a'magnetic body comprising finely dividedmagnetic "CR SS mamas" body having a low eddy current loss from a givenamount of finely divided ma etic material and a given amount of a fineinsulatin and binding material mcluding both solu 1e and insoluble inredients, which method consists in mixingt e total amount of themamietic material with a'portion of the insoluble ingredients of theinsulating and binding material in dry form, adding to the mixture aliquid solution of a portion of the solubleingredients of the insulatingand binding material and evaporating the whole to dryness with constantstirring mixing. the resulting coated magnetic particles with anotherportion of said insoluble ingredients in dry form; addin to theresulting mixture 9. liquid solution 0 another portion of said solubleingredients and evaporating the whole to dryness with constantstirring,- repeating the rocess until all of the insulating an bindingmaterial has been applied as coatin s to the magnetic particles,compressing t e resultant product into a substantially h0- mogeneousmass in the desired 'form, and then heat treating the formed product toremove strains in the ma etic material.

4. In the process 0 makin a magnetic body comprising finely dividedparticles of magnetic material insulated from each other by a givenamount of insulationcomprising several constituent materials, the methodof insulating the magnetic particles which consists in mixing in avolatile liquid said mag- Examiner divided netic particles with aportion of the insulation comprising a portion of each of theconstituent materlals and evaporating the mixture to dryness, mixing theresulting product in a volatile liquid with another portion of theinsulation'comprising a portion of each constituent material andevaporating the mixture to dryness, and repeating this process until theentire amount of the insulation has been applied to the magneticparticles in successive layers.

In witness whereof, I hereunto subscribe my name this 1st day of'July,1931. v

.HUBBEL LATHROP.

particles insulated from each other by a given amount of insulatingmaterial, the method of insulating the magnetic particles which consistsin mixin said magnetic particles with a portion of t e total amount ofinsulating material in a volatile liquid and evaporat ing the mixture todryness'to form an insulating coating on the particles, mixing thecoated particles with another portion of the insulating material in avolatile liquid and evaporating the mixture to dryness to form a appliedto the magnetic articles in layers;

. 3.The method. of pro ucin'g a magnetic second layer of insulatingmaterial on the

